# Gravity Hot Water Recirculating Loop Questions

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#### HarleySilo

##### New Member
So I have to wait too long for hot water. I've been looking at recirculating pumps, various brands, various methods. Read and article about gravity hot water recir. loops. I understand the theory, but am wondering if two loops can work.

Cliffs on info:

You run a return hot water line from furthest fixture. You plumb it into the hot water heater's drain spigot. You remove any backflow preventer on the hot water supply side. Thermal properties of heated water take over and hot water rises out of HW heater and the cooler water in the return lines "sinks" into the bottom of your water heater. This slow circular motion keeps hot water available at furthest point. You must insulate the lines, except for last 15ft of return.

So my water lines look like the below diagram, but I would like Hot water at both ends of the line, and am wondering if two loops would work, and if so how to plumbe them correctly.

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#### HarleySilo

##### New Member
So I found another article...
http://www.contractormag.com/articles/column.cfm?columnid=62

Main thing I picked up on is it states I should add the volume of water now contained in the loop to my calculation for the expansion tank size....

So for me one loop of 100' of 3/4 would be approx....5 gallons.....

#### Geniescience

##### Homeowner
two loops, yes.

(no i am not an expert at this.)

yes, more than one loop will work just as well as only one loop. They are each independent of each other, and do not cause dependencies on the hot water heater. (A linear system, a linear sum.) True, that total number of loops possible is eventually an issue, because hot water is limited, but this is moot here as only two loops are suggested. Unless your HW heater is real small... and your loops are real long ... i wouldn't worry unless you say more that makes me say the opposite.

to make lighter fluids rise, the geometry is to put the first half of the loop higher than the second half of the loop. First half being fully heated water, second half being return water, which less hot, more "cold", thus denser, it will fall down into the lower pipe, which you have positioned to be lower. More about this in general, under Convection in Wikipedia. To make the colder half be truly colder you could stop insulating it soon after the end point, which may be a far greater distance than 15' from the end of the return.

2.) An alternative to a HW convection loop: There are also systems proposed that use the existing cold water pipe as the return pipe. When you turn on cold water, you DO get cold water from the cold entry into your house, but initially you get the warm water than is on its way back to your HW heater.

david

#### HarleySilo

##### New Member
hummmm, theoretically I have to agree with your statements.

You brought something up I had overlooked, the return line must be lower.

I was just concentrating on where it terminated, not the path it takes. However the question remains, what is the minimum distance the return pipe must be from the supply. Must that distance be constant, or can half the run be side by side, and the last half the run distance increase. I thought once the flow started, even if just in one section suction would help to pull it along.

Here, quick pic

Would both work?

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#### Geniescience

##### Homeowner
yes, both will work

harley

yes, inertia will carry water forward. And as soon as you turn on the tap the first time, just once, you will set inertia into play since the loop is an open loop and the head of water will kick-start the circulation. Turning the tap off the first time sets the loop into motion. Even without this, suction would also make the loop move, too, afaik.

Both loops will work because a significant segment is oriented to create the convection flow.

david

#### HarleySilo

##### New Member
So I went with a Recir pump. Installed it, insulated the 50' run of copper pipe from water heater to kitchen sink, and installed the valve.

Results

no pump
hot water arrives anywhere from 30-50 seconds.
Cold water immediate

with pump
warm water arrives within 2 seconds
hot water arrives within 15 seconds
Cold water is almost immediate, it is warm for 2 seconds

So i'm still "adjusting" the timing on the pump, i have it running for 30 mins. out of every hour for the time being. 15 mins. out of every hour was not enought to make a noticeable difference.

I still might run a return line, and use the pump continuously. If I do run the line, do I plumb it to the bottom spigot of the water heater? That's the only way it makes sense to me otherwise I would just be recir-ing water in a loop, never getting new hot water added in unless someone used some.....thoughts?

#### Plumb or Die

##### Plumbing Instructor
Cut a tee into the cold inlet to the tank. Install a swing check valve on the cold inlet before the tee. Run the recirc. to the other hole in the tee. Wish I had CAD so I could draw you a picture. That's the way to plumb a recirc. line.

#### hj

##### Master Plumber
pump

By "recirc pump" do you mean a Grudfos Comfort or Laing AutoCirc? If so, then you should have a "manifold" under the farthest sink(s), to control the amount of hot water that enters the cold line, so you can either run the pump continuously, because there will not be any flow when it is not needed, or run it when you might be using hot water.

#### Cort

##### New Member
I have a single story house-will it work?

My water heater/solar shed is above the level of house hot water lines-will this system work for me- as the hot water has to drop under the level of the water heater to get under the house
My water heater already has a ball valve on outlet/drain so plumbing a return 3/4 copper line is a snap-the total return run is less than 30 feet from furthest bathroom. Cort

#### Redwood

##### Master Plumber
You would be limited to a pumped recirculation system.

#### hj

##### Master Plumber
circulation

The water has to flow upwards from the heater, and downwards from the furthest point. AND the upward and downward flows must be continuous without any up or down jogs. The circulation will cease immediately if their is a drop in the upward flow or rise in the downward flow.

#### Mitchr

##### New Member
Response to Master Plumb

Hello, I've been thinking about this same topic lately and also would like to install a recirculating loop in our home system. I like the idea of the swing check valve that was posted earlier. Do you o others have any comments on whether or not this a good way to go. Out hot water heater has a turn valve at the bottom and I would rather not connect to it. Thanks, Mitch

#### Cort

##### New Member
Any suggestions on what brand of pump for a pumped recirculation system ?I would like to hook it to a timer for optimum times.
I have a spare grunfus or taco from a solar system I took out -or are there better options now?. Cort

My water heater/solar shed is above the level of house hot water lines-will this system work for me- as the hot water has to drop under the level of the water heater to get under the house
My water heater already has a ball valve on outlet/drain so plumbing a return 3/4 copper line is a snap-the total return run is less than 30 feet from furthest bathroom. Cort

#### hj

##### Master Plumber
check

ANY circulation system with a separate return pipe, MUST have a check valve regardless of where it is connected back to the tank.

##### Retired Defense Industry Engineer xxx
If the circulated water is potable water, the pump must be a bronze or ss body. All of the companies make both iron and bronze pump\$. Don't remember is this is strictly a (closed) heating loop, or if it is potable water you're moving around.

#### Furd

##### Engineer
Yep, stainless steel or bronze pump. I would be leery of using a pump that had ever been used with an anti-freeze solution.

#### Leejosepho

ANY circulation system with a separate return pipe, MUST have a check valve regardless of where it is connected back to the tank.

Yes, or else an open hot-water faucet can be fed from both lines.

#### Cort

##### New Member
Mine would be potable hot water loop-and yes I'd put in a check valve on the loop. I have an older open (sunspool) loop solar system feeding an 80 gallon solar tank feeding the hot water heater the past 24 years.I would only use S/S or bronze pumps. Cort

If the circulated water is potable water, the pump must be a bronze or ss body. All of the companies make both iron and bronze pump\$. Don't remember is this is strictly a (closed) heating loop, or if it is potable water you're moving around.

#### samsonn

##### New Member
I have read the posts on these systems and I am a bit confused as to what the "return" pipe size should be. In my case the house is a 2 story cottage with a basement. the hot water tank is in the basement and the original 1/2" copper pipiing was upgraded to 3/4" copper. I recently added some additional surround massage jets when I redid the shower enclosure and added a 3/4" PEX line to the upper floor with some manifiold type arrangement to increase the water flow. I would like to run a small PEX at the end of line (which is still 1/2" copper) back to the tank. PEX is somewhat insulated so I can snake it around and not cause too much damage. My question is can I use 3/8" PEX or 1/2" Pex and then use copper for the last 15 ft and what would be the effect of using a larger diameter copper (For the last 15 ft) with the 3/8" pex? I want to trickle the flow so 3/8" would be enough if I used a pump but would this work with gravity/convection. This seems a bit of a physics question, do u have any suggestions?

#### McconnellPlumbing

##### Scotsman
If a swing gate type check valve is installed, and the circulating pump runs most or all the time, the gate often gets stuck in the open position. Then it allows for the water to run backwards from intended flow direction unless the pump is on and is forcing the water a certain direction. A spring loaded check valve would be better.

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